Recently, as optical access systems, optical communication systems have been adapted as a mainstream which has a transmission capacity of 1 Gbps class (hereinafter, “Gbps” may be simply referred to by “G”) which accommodates a plurality of subscribers in the passive double star configuration, such as the gigabit Ethernet-PON (GE-PON), the gigabit capable-PON (G-PON).
As next-generational PON systems, adapting communication systems having a transmission capacity of a 10 G have been studied for increasing the communication speed. In addition, for the strategy to extend service ranges, increasing the length and the number of branches by adding repeaters (relay apparatuses) has been studied.
In developing such PON systems, network systems that allow coexistence of systems having different transmission speeds is expected for transitioning to a system in which the transmission speed is increased in a more economical and efficient manner. Such systems include, a system in which a 1-G system and a 10-G system coexist. Even in such a network system, it can be assumed that repeaters are used in order to increase transmission distance.